An image forming apparatus, such as a laser printer, is generally includes a fixing device for thermally fixing an image transferred to the sheet from a photosensitive element. JP-A-8-48432 discloses a fixing device including a heating roller heated by a heat source, a pressing roller pressed toward the heating roller, and a bearing that rotatably supports the heating roller and that is formed of a conductive resin. According to this device, an earth plate is connected to the bearing formed of conductive resin, thereby allowing electric charges accumulated in the heating roller to be discharged. Depending on the structure of the fixing device, there is a case where a conductive member for supplying power to the heat source and a power supply member having a thermal fuse as a safety device are disposed in the vicinity of the bearing of the heating roller.
However, in a case where the bearing is formed of a conductive resin and the power supply member is disposed in the vicinity of the bearing, when the bearing has become fused as a result of occurrence of a failure in temperature control of the heating roller, the fused bearing may contact the power supply member. When the bearing contacts the power supply member as mentioned above, a short circuit arises between the power supply member and the heating roller by way of the conductive bearing. This may eventually result in infliction of damage on the fixing device.